298 W. J. CROZIER 



I. INTRODUCTION 



Holothurians possessing respiratory trees are provided with a 

 cloacal chamber which acts as a pump supplying these organs 

 with sea water. The most obvious manifestation of this activity 

 is the rhythmic opening and closing of the anus. This pulsa- 

 tion has never been studied in detail, ^ though it presents morpho- 

 logical and physiological features of considerable interest. 



I have previously (Crozier, '15) brought forward reasons 

 for believing that the cloacal region of a typical aspidochirote 

 holothurian, H. surinamensis, contains within itself the essential 

 mechanism of its pulsation, though there is, superimposed upon 

 this independently pulsating complex, a control of its activity 

 by the animal as a whole. It was found that rhythmic cloacal 

 movements were maintained for about three days in the case of 

 small pieces cut from the aboral end of H. surinamensis, but that 

 in the excised pieces pulsation was continuous and failed to 

 exhibit certain interruptions which are characteristic of these 

 movements in the intact animal. It was noted that Edwards 

 ('09, p. 215) recorded the observation of anal movements in the 

 larvae of H. floridana before the appearance of the respiratory 

 trees. Therefore it seemed that the anal pulsating mechanism 

 might be regarded as constituting another unit in the series of 

 independent effectors, such as pedicellariae and spines, which go 

 to make up the echinoderm neuro-muscular equipment. 



The ability of the isolated posterior ends of pedate holothurians 

 to maintain their pulsation for relatively long periods I have 

 further verified by observations upon the following species occur- 

 ring at Bermuda: Cucumaria punctata Ludw., Holothuria cap- 

 tiva Ludw., H. rathbuni Lamp., and Stichopus moebii Semper. 



The problem of the present investigation was to determine the 

 physiological characteristics of cloacal pulsation in holothurians, 

 particularly in the case of the aboral ends removed from the 

 control of the animal as a whole by amputation ; and to discover 

 to what extent the laws of rhythmic movement, especially as 



- The early observations on the pumping activity of the holothurian cloaca 

 are collected by Ludwig ('89-92, p. 387). 



